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Chapter 16.12 : Q Fever—Coxiella burnetii
Coxiella burnetii is the etiologic agent of Q fever. It is a pleomorphic coccobacillus that is gram negative, obligately intracellular, and 0.3 to 0.7 µm long. There is a spore-like form, the small cell variant, which is remarkably stable in extracellular environments. A large cell variant also exists that is the vegetative, metabolically active form. Mixtures of both forms are found in phagolysosomes. There is phase variation, similar to that in Salmonella, in which the lipopolysaccharide (LPS) varies chemically as either the virulent, phase I “smooth”-type LPS or the phase II “rough” LPS, associated with avirulent C. burnetii. C. burnetii is phylogenetically related to Pseudomonas, Francisella, and Legionella, within the Legionella group of the c-Proteobacteria subdivision. It is more distantly related to Rickettsia ( 7 ).